Semiconductor manufacturing processes generally involve the use of Chemical Vapor Deposition during processing of dielectrics and metals. Certain parts of the manufacturing process also etch semiconductor components with chemical vapor, which typically consists of perfluorinated compounds (PFCs) and fluorine gas. The steps of the manufacturing process are typically achieved by specific tools, which are generally cleaned after a number of cycles. In many industrial processes, such as semiconductor manufacturing, some amounts of fluorine gas remain unutilized.
Fluorine gas is highly corrosive, and both elemental fluorine and the fluoride ion can be highly toxic. Accordingly, it is desirable to safely and efficiently remove and properly dispose of fluorine and/or fluoride used in industrial processes, and in semiconductor manufacturing processes in particular.
Current technologies for fluorine removal focus on scrubbing the fluorine gas with simple air scrubbers to produce a constant bleed of hydrofluoric acid (HF), which is generally sent to a manufacturing facility's Acid Waste Neutralization (AWN) system for processing and disposal. Because HF is a weak acid with a pKa of 3.16, the transformation of F2 to HF is discouraged at low pH values. This becomes problematic for scrubbers, as pH becomes the controlling mechanism for bleed volumes and consequently for concentration of HF. Further, increasing pH, such as by addition of alkali, poses further problems because OF2, an undesirable byproduct, can be produced in an alkaline environment in the presence of hypofluorous acid (HOF), which is also formed during the reaction of F2 with water. Additionally, despite operating at maximum allowable concentrations of HF in the scrubber, the HF reaching the AWN is generally too dilute for optimal operation of fluorspar (CaF2) precipitation systems. Further, large amounts of chemicals are consumed in conventional CaF2 precipitation systems. Additionally, the sludge volume is very high due to the high level of hydration, requiring excessive CaF2 sludge hauling.
Accordingly, there remains a need to provide a new and improved method and apparatus for removing and collecting fluorine and/or fluoride. There further remains a need for a system for removing fluorine which has a low operating cost and which generates a concentrated end product that can be hauled away economically. The present invention is directed to meeting these needs.